Implantable electrical stimulation devices have been developed for therapeutic treatment of a wide variety of diseases and disorders. For example, implantable cardioverter defibrillators (ICDs) have been used in the treatment of various cardiac conditions. Spinal cord stimulators (SCS), or dorsal column stimulators (DCS), have been used in the treatment of chronic pain disorders including failed back syndrome, complex regional pain syndrome, and peripheral neuropathy. Peripheral nerve stimulation (PNS) systems have been used in the treatment of chronic pain syndromes and other diseases and disorders. Functional electrical stimulation (FES) systems have been used to restore some functionality to otherwise paralyzed extremities in spinal cord injury patients.
Typical implantable electrical stimulation systems may include one or more programmable electrodes on a lead that are connected to an implantable pulse generator (IPG) that contains a power source and stimulation circuitry. However, these systems can be difficult and/or time consuming to implant, as the electrodes and the IPG are usually implanted in separate areas and therefore the lead must be tunneled through body tissue to connect the IPG to the electrodes. Also, leads are susceptible to mechanical damage over time, particularly as they are usually thin and long.
Recently, small implantable neural stimulator technology, i.e. microstimulators, having integral electrodes attached to the body of a stimulator has been developed to address the disadvantages described above. This technology allows the typical IPG, lead and electrodes described above to be replaced with a single integral device. Integration of the lead has several advantages including reduction of surgery time by eliminating, for example, the need for implanting the electrodes and IPG in separate places, the need for a device pocket, the need for tunneling to the electrode site, and requirements for strain relief ties on the lead itself. Reliability may therefore be increased significantly, especially in soft tissue and across joints because active components, such as lead wires, are now part of the rigid structure and are not subject to the mechanical damage due to repeated bending or flexing over time.
Unfortunately, the currently developed leadless devices tend to be larger and more massive than desirable, and even than traditional electrode/lead assemblies, making it difficult to stably position such devices in the proper position with respect to the nerve. Without device stability, the nerve and/or surrounding muscle or tissue can be damaged due to movement of the assembly. Further these devices require long charging times, and are often difficult to control (e.g., program) and regulate. There remains a need for leadless integral microstimulator devices that can be stably positioned on the nerve and regulate their power, including power delivered by an outside charger to inductively charge the implant.
The power requirement of implantable neurostimulators may be highly limiting. The greater the power required, the longer the charging time, and the larger the implant (e.g., battery, capacitor, etc.) must be. In addition, because these devices are implanted, they must be protected or constrained from heating above internal body temperature more than a minimum amount (e.g., 2° C.), or risk damaging tissues. This may be particularly challenging when inductive charging is used to charge the implant.
Moreover, there might be unexpected situations such as circuit dysfunction or failure, sudden health condition change of the patient, unusual environment, thermistor failure, etc. A manual shut-off of the microstimulator may be needed in such emergency situations. There is a need for a manual shut off of the implantable microstimulator to protect the patients in case of emergency.
Described herein are microstimulators (MS, also referred to herein as neurostimulators, microregulators, MRs, etc.) and methods of using them that may address some of the needs identified above.